How Does Your Electric Motor Measure Up?

  • Motor

Is your motor shop still using dial indicators to measure the critical components of electric motors? Are you afraid that you may have insufficient knowledge with motor measurements? Not a problem! Cascade Machinery Vibration Solutions has created a system to measure the bore to stator centerline; stator and bearing bore ovality; feet co-planer and parallelity to stator centerline. Using the Easy-Laser® geometric system, these measurements can now be electronically collected without the need for extensive setup.

In order for the potential Easy-Laser® users to better understand the value and efficiency of the products, Cascade worked with Integrated Power Systems (IPS) to perform a complete measurement of an electric motor alignment at the IPS shop in Beaumont, TX.

Electric motors should be inspected regularly, at least once every 5-6 years with the goal to prolong motor life and performance. Gene Steadman, Service Center Manager of IPS Beaumont, TX motor shop, suggests: “if there is vibration at certain harmonics or frequencies, then this is giving an indication that there are problems developing in the motor. The problems can be either internally or externally caused.”

Three key measurements for electric motor reliability are:

Air Gap

Air gap is the space between an electric stator and a rotor. The ultimate goal in measuring the stator is concentricity within 10% of the total diameter and air gap from stator to rotor. Internal alignment is making sure all the air gaps between the electric stator and rotor are equal. Most motor shops check air gaps by using feeler gauges, and it is very critical to make sure that all the air gaps are equal all the way around. If all machine fits and within tolerance, the air gaps would be equal. However, if the air gaps are not equal, the motor would exhibit vibration problems or not operate correctly.

Base Foundation

After a motor has been in service and operating for several years, there could be potential frame distortion, foundation settling or base issues which cause machine parts to come out of alignment. For example, if a machine was mounted on a cracked floor (an external cause of misalignment), the frame might be distorted, and this could affect the stator to be no longer operating at the center line. Moreover, the face of the frame also needs to be perfectly perpendicular to the center line. In other words, if the frame is not in a right angle with the center line, then the electric stator would also be out of tolerance.

Center Line

To ensure all air gaps are equal, the essence of performing an electric stator alignment is to keep all the machine parts true to the center. In other words, we assume that an electric stator is true and round, the motor frame and bearing landings are square to the center line; the stator, the rotor o.d (i.e. the outside dimension), and the bearings shaft are all within tolerance and .002”- .003” per inch of true.

In IPS motor shop, the Cascade team established the center line of a motor by simply and precisely measuring seven planes along the two sets of the bearing landings and the electric stator.

During the process, the laser beam establishes the center line between two reference points, and each plane was recorded five to seven times to maximize the precision of the measurement. A laser beam was also shot in a right angle to determine the condition of the face of the frame. Data collected was generated by the Easy-Laser® program and auto saved to a PDF file for further analysis.

As a result of the measurement:

  • The electric stator was misaligned to the center line of the bearing landings.
  • The face of the frame was distorted, which did not appear to be perpendicular to the center line of the bearing landings.
  • One of the bearing landings was also found to be slightly lower than the other one.

The total time cost for Cascade to diagnose the misalignment of this electric stator was within four hours. The data was stored and will be a reference for future motor repair and maintenance. The easy setup of Easy-Laser® tools and their ability to document raw data and statistic reports not only reduce the cost of resources, but also significantly improve the proficiency and credibility of motor shops or end-users.

Troy Broussard, the President of Cascade MVS noted: “think of the Easy-Laser tool systems as extra insurance and peace of mind when it comes to your large, expensive motors”. In the past, there was no simple solution for ensuring the complete repair of these motors. Now there is.

 

 

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